Material for refining steel of multi-purpose application

ABSTRACT

The claimed material for refining steel of multi-purpose application contains the following components in the following proportion, % by mass: 
     
         ______________________________________                                    
 
    
     aluminium     30-40                                                       
silicon       35-25                                                       
calcium        5-15                                                       
magnesium     7-5                                                         
carbon        20-10                                                       
iron          the balance.                                                
______________________________________

TECHNICAL FIELD

The invention relates to metallurgy and has specific reference to thematerials for refining steel of multi-purpose application.

BACKGROUND OF THE INVENTION

Steel of multi-purpose application is a term used in reference to thesteel of the following composition, % by mass:

    ______________________________________                                        carbon              0.05-0.5                                                  manganese           0.25-2                                                    iron                the balance.                                              ______________________________________                                    

Steel of multi-purpose application may also contain (% by mass) suchelements as:

    ______________________________________                                        silicon              up to 0.6                                                aluminium            up to 0.08                                               chromium             up to 2                                                  vanadium             up to 0.2                                                titanium             up to 0.2.                                               ______________________________________                                    

The presence of other elements is not excluded as well.

In world steelmaking practice, confined to the ladle are now thefollowing operations: alloying, desulphurisation, modification and theremoval on nonmetallic inclusions, degassing, i.e. the reduction ofoxygen, nitrogen and hydrogen content.

The alloying and refining are carried out in succession. The steel isalloyed by adding various ferroalloys and then it is refined by suchtechniques as the application of vacuum or the introduction of powderedmaterial with the aid of a jet of an inert gas.

Considerable heat losses are involved during each operation of alloyingand refining. To compensate for the losses, the metal must be overheatedin the furnace and tapped at a temperature above normal or it must beheated up in the ladle, using certain means.

However, both ways are irrational in the making of steel formulti-purpose application. Firstly, an increase in the solubility ofoxygen at high temperatures results in a higher than normal oxidation ofthe metal. This calls for using more deoxidisers which contaminate thesteel by the nonmetallic inclusions resulting from the reaction andimpair product quality. Secondly, the extra heating up with specialmeans adds to the costs, for such means must be purchased and installed,and also extends the period of treatment, reducing plant capacity.

All in all, the cost of steel rises--a fact which is not justifiable asfar as the production of steel for multi-purpose application isconcerned.

Known in the art is a material for the refining of molten metal (EP, A1,0192090) which has a composition (% by mass) as follows:

    ______________________________________                                        silicon          40-80                                                        titanium         10-20                                                        magnesium        1.5-3                                                        calcium            0-0.5                                                      aluminium        0-2                                                          rare-earth elements                                                                            0-2                                                          iron             the balance.                                                 ______________________________________                                    

However, the known material is ineffective in removing sulphur andnonmetallic inclusions, for the percentage of the oxygen dissolved inthe molten metal is low.

The content of reactive agents, i.e. deoxidisers--aluminium, magnesium,calcium and rare-earth elements--which are also strong desulphurisingadditives and strong modifiers of nonmetallic inclusions, is low in theknown material. The available deoxidisers effectively eliminate theoxygen dissolved in the molten metal when the known material is addedthereto but they appear to be in short supply for the desulphurisationand modification to take place.

Apart from that, the titanium which is present in the known material forrefining forms high-melting oxides. Rising to the surface, these oxidesrender the slag more viscous and less effective as the sorbent ofsulphur and nonmetallic inclusions. These unwanted substances remain inthe metal, impairing the quality thereof.

The known refining material, if used as the source of alloying elementsreduced form oxides contained therein, is of no avail in producing metalof a conditioned composition. The silicon contained in the knownrefining material has a high affinity for oxygen but it is also areducing agent of a strength inferior to that of aluminium, magnesiumand calcium. Therefore, the reaction yields acidic oxides of siliconwhich increase the viscosity of the slag and reduce the reactivity ofthe alloying element contained in the slag. This has an adverse effecton the reduction of alloying element. Also, the process ofdesulphurisation is difficult due to an impaired ability of the slag toremove sulphides and act as the sorbent of nonmetallic inclusions.

All the above factors spoil the quality of steel. Also known is amaterial for refining (SU, A, 456,032) of the following composition, %by mass:

    ______________________________________                                        manganese     48-60                                                           silicon       28-32                                                           aluminium      6-12                                                           calcium       0.4-3                                                           magnesium     0.3-2                                                           carbon        0.06-0.3                                                        phosphorus    0.04-0.35                                                       sulphur       0.01-0.02                                                       iron          the balance.                                                    ______________________________________                                    

However, this material cannot boast good results as far as the degree ofdesulphurisation and removal of nonmetallic inclusions is concerned.

The explanation is the qualitative and quantitative composition of theknown material. In the first place, the percentage of the elements witha high affinity for oxygen--such as calcium, magnesium, aluminium andsilicon--is low.

In the second place, it contains phosphorus and sulphur which areunwanted admixtures.

In the third place, there is an abundance of manganese which reacts withthe sulphur to form a low-melting manganous sulphide--a substance whichreadily dissolves in the molten metal and interfers with the slagging ofsulphur.

In the fourth place, the carbon is present in the known material as anadmixture so that extra carbon is required for refining the metal. Thisinvolves an increase in the sulphur content of the metal and a degradingof product quality.

The use of the known material as an oxide-containing alloying additiveis impractical. Although, there are elements which eagerly react withthe oxygen of oxides, their percentage is low. The degree of reductionis consequently low as well so that no steel of specified compositioncan be produced. Desulphurisation and the removal of other nonmetallicinclusions are totally absent so that no quality stell can be made.

SUMMARY OF THE INVENTION

The principal object of the invention is to provide a material forrefining steel of multi-purpose application which will improvedesulphurization of steel and removal of nonmetallic inclusionstherefrom by using a certain proportion of its components.

This object is realized by disclosing a material for refining steel ofmulti-purpose application containing aluminium, silicon, magnesium,carbon and iron, wherein, according to the invention, these componentsare present in the following proportion, % by mass:

    ______________________________________                                        aluminium     30-40                                                           silicon       35-25                                                           calcium        5-15                                                           magnesium     7-5                                                             carbon        20-10                                                           iron          the balance.                                                    ______________________________________                                    

The disclosed material is suitable for refining steel in the course ofalloying which is being accomplished by either adding ferroalloys orreducing the alloying elements from their oxides.

The disclosed material for refining steel of multi-purpose applicationpermits the making of steel with a minimum content of sulphur and othernonmetallic inclusions. This is achievable owing to the presence of morethan one element with a maximum affinity for oxygen.

The fact that these elements are present in the specified proportioncares for the deoxidation to take place concurrently with an unhinderedshaping of globules of the nonmetallic inclusions which are disposed ofeventually with the flushing slag. Passing over into the slag are thesulphides resulting from the desulphurization of steel of multi-purposeapplication which occurs also at the same time.

These steps are conducive to improving the quality of steel ofmulti-purpose application.

The disclosed material for refining may be employed in the form ofeither mixture or alloy. The mixture can be composed of pure materialswith a maximum content of the principal element. Pure materials can bemixed with compounds, e.g. carbides of calcium or silicon or thesecarbides can be mixed with an aluminium-, magnesium-or iron-bearingalloy.

It is expedient to employ the disclosed material for refining duringladle treatment of the steel for multi-purpose application.

It is also preferred to employ the disclosed material in alloying steelwith manganese which is reduced from the material containing themanganese in the form of oxides.

The slag formed during the process of refining is a free-running onewhich readily separates from the metal. It is also a good sorbent ofsulphur and nonmetallic inclusions. Apart from that, the slag is a goodheat insulator which gives the metal a reliable protection againstcooling and secondary oxidation. A quality steel with a low content ofsulphur and nonmetallic inclusions is so produced.

The disclosed refining material is rich in elements reactive towardsoxygen which deoxidize the metal in the ladle and reduce alloyingelements from the oxides. Desulphurization and the removal of othernonmetallic inclusions take place at the same time.

An addition of a material with oxides of the alloying element to thedisclosed refining material prevents the burning-out of the elementsreactive towards oxygen which are contained in the disclosed refiningmaterial.

The material containing oxides of the alloying element rapidly dissolvesin the ladle and forms a layer of slag which prevents oxidation of theelements having affinity for oxygen by the oxygen of the atmosphere.

Concurrently with the reduction of the oxides of alloying elementsspreading uniformly over the volume of the metal, the process ofrefining goes on. The reactions are exothermic ones so that there is noneed to preheat the metal in the furnace or ladle. This not onlyimproves product quality but saves cost.

An aluminium and silicon content of the disclosed refining materialamounting to 30-40 and 25-35%, respectively, fully meets therequirements of metal deoxidation. This creates favourable conditionsfor desulphurization and provides for a percentage recovery of thealloying element from the oxide which is as high as 95%. Complexaluminium and silicon compounds formed in this case readily rise to thesurface. Being of the low-melting nature, they do not impair thefluidity of the slag and have therefore no adverse effect on the sorbingpower thereof.

An aluminium content of the disclosed refining material which is lessthan 30% calls for rising the silicon content up to over 35% and hastherefore an adverse effect on the reduction of the alloying elementfrom its oxide. The percentage of bisilicates--products of oxidation ofthe silicon--increases in the slag and the reactivity of the alloyingelement contained in the slag decreases. The slag gets viscous, the masstransfer therein gets worser and the sorbing power of the slag withrespect to sulphur decreases. The steel quality is degraded.

An increase in the aluminium content over 40% reduces the siliconcontent below 25%. This is impractical, preventing an increase in thepercentage recovery of the alloying element. Alumina inclusions increasein the steel, impairing its quality.

Also, the cost of the refining material increases, adding to the firstcost of the steel. This is not justifiable in the production of steelfor multi-purpose application.

A calcium content of the disclosed refining material which is between 5and 15% is conducive to obtaining low-sulphur steel. Thecalcium/magnesium combination produces a morphological effect, givingrise to uniform distribution of the nonmetallic inclusions in the formof globules.

A calcium content under 5% prevents the production of low-sulphur steeland is incompatible with product quality.

An introduction of calcium in an amount exceeding 15% of the materialinvites difficulties stemming from high vapour pressure and goodaffinity for oxygen which are inherent un calcium. But the main thing isthat high calcium content does not improve product quality. No furtherdecrease in sulphur content takes place but the cost of the material andthat of the steel rises.

A magnesium content of the disclosed refining material al which is 5-7%is conducive, in combination with the calcium, to a low sulphur contentof the steel. The nonmetallic inclusions diminish in size, acquireglobular form and uniformly distribute over the volume of the metal.This has a positive effect on product quality.

A magnesium content under 5% is too low to have an influence on themodification of nonmetallic inclusions. A content over 7% has no bearingon product quality.

A carbon content of the disclosed refining material which is 10-20%provides for alloying the steel with the carbon with a high percentagerecovery. Some of the carbon goes to deoxidize the metal withoutcontaminating it, for the product of the reaction is a gas-carbonmonoxide. A high degree of metal deoxidation paves the way effectivedesulphurization and the removal of other nonmetallic inclusions.

A carbon content under 10% makes an addition of extra carbonunavoidable. The sulphur which is added in this case with thecarboniferous material increases the sulphur content of the steel,degrading its quality due to the presence of sulphide and oxysulphideinclusions.

A carbon content over 20% makes the disclosed material not quitesuitable in treating low-carbon steel. Insufficiency of the compoundstaking an active part in the process of refining the steel is anotheraftereffect.

An iron content of the disclosed material which is 5-15% is exactly onewhich is needed in order to impart the material a density enabling it tosink to the metal-slag interface. The alloying elements are reducedthere from the oxides contained in the slag.

An efficient refining of the metal to remove sulphur and othernonmetallic inclusions therefrom takes also place. The specified carboncontent facilitates the introduction of carbon into the disclosedrefining material when this is being used in the form of alloy, for theiron increases the solubility of the carbon.

An iron content under 5% fails to introduce carbon into the refiningmaterial in a requisite amount and reduces the density of the materialwhich can stay in the slag. The elements which are reactive towardsoxygen burn out in this case.

An iron content over 15% is not desirable. The density of the refiningmaterial excessively increases and the material sinks deep into themetal. This badly affects the process of reduction of the alloyingelements which is confined to the slag-metal interface anf reduces thecontent of the elements reactive towards oxygen and sulphur. A degradingor product quality is inavoidable.

It is also expedient to introduce rare-earth elements into the disclosedrefining material. Being extremely active with respect to the elementsof introduction--O₂, N, H, S--the rare-earth elements owe theirmodifying and refining power to this property. The modifying power isattributed to surface tension variations at the interface between theliquid and solid phases. This affords control over the process ofprimary solidification so as to change the degree of dispersion of thesolidifying phases. A dispersed heterogene structure of the cast steelis a prerequisite of fine-grained structure of the rolled product.

Apart from that, the free energy of rare-earth sulphides is morenegative than that of sulphides of other metals. For example, no easilydeformable manganous sulphides would form in the presence of rare-earthelements, for it is the turn of the inclusions--sulphides of rare-earthelements--which form before all and only then come the complexoxysulphide inclusions which give no rise to threads in the course ofrolling. The presence of rare-earth elements in steel in the specifiedamount prevents flocculation.

It is advisable that the composition (% by mass) of the material forrefining steel of multi-purpose application is as follows:

    ______________________________________                                        aluminium        30-40                                                        silicon          30-25                                                        calcium          15-5                                                         magnesium        5-7                                                          carbon           10-20                                                        rare-earth elements                                                                            5-1                                                          iron             the balance.                                                 ______________________________________                                    

A reduction of the silicon content of the disclosed refining materialfrom 35-25 to 30-25% by mass provides for decreasing the total amount ofnonmetallic inclusions, i.e. silicates, which are present in the steel.The rare-earth elements introduced additionally in an amount of 1-5%serve as modifying additives dispersing the remnants of nonmetallicinclusions, such as hercynite (FeO.Al₂ O₃), CaO.Al₂ O₃, Al₂ O₃ and thelike. The outcome is low-sulphur quality steel which containsnonmetallic inclusions of favourable shape and composition and acquiresfine-grain structure when rolled.

It is desirable that the disclosed material for refining steel ofmulti-purpose application is of the composition (% by mass) as follows:

    ______________________________________                                        aluminium        30-40                                                        silicon          35-25                                                        calcium          15-5                                                         magnesium        5-7                                                          carbon           10-12                                                        rare-earth elements                                                                            1-2                                                          iron             the balance.                                                 ______________________________________                                    

A reduction of the carbon content of the disclosed refining materialfrom 10-20 to 10-12% by mass widens the field of application of thematerial, rendering it suitable for treating low-carbon steel with acarbon content of 0.1% by mass or less. The rare-earth elementsintroduced additionally in an amount of 1-2% by mass act as a grainrefining agent. They also enhance the desulphurizing effect of othercomponents of the material which show high affinity foroxygen--aluminium, silicon, calcium and magnesium--and take care of deepladle deoxidation as well as desulphurization of the metal. Thedesulphurizing and refining properties of the rare-earth elements reducethe content of nonmetallic inclusions and add to the quality of steel.

To adapt the process of preparing the disclosed refining material forstreamlined operation and reduce cost, it is recommended to introducecalcium, silicon and carbon in the form of commercially availableproducts, e.g. carbides of calcium and silicon. These materials areinexpensive and pose no handling and storing problems.

While calcium carbide is a good desulphurizing and carboniferous agent,silicon carbide promotes slag-making, speeds up desulphurization and isan effective sorbent of nonmetallic inclusions.

The disclosed material for refining steel of multi-purpose applicationmarkedly improves product quality by virtue of decreasing the content ofsulphur and nonmetallic inclusions.

Best Mode for Carrying Out the Invention

The disclosed refining material is prepared on the following lines.

A 5-ton charge of aluminium and magnesium is heated to 600°-650° C. inan induction furnace, and an inert gas atmosphere is set up at thesurface of the melt before this is heated to 1000°-1100° C. and iron isadded to the bath. The molten metal is homogenized, cooled to 550°-600°C. and cast into cast iron trays. On cooling down, the material iscomminuted as required. A vacuum induction furnace operating at the sametemperature can be used to prepare the refining material.

The ground material is mixed with carbides of calcium and silicon andplaced into the ladle assigned for removing sulphur and othernonmetallic inclusions from steel of multi-purpose application.

The disclosed refining material is used in the following way. Thematerial liable to refining can be made in a plant of any known kind:open-hearth furnace, electric furnace or a converter blown at the top,bottom or both at the top and bottom whereby the blast may consist of amixture of oxygen with a gas, an inert gas or a mixture of inert gases.

The metal tapped from the steelmaking plant is a semifinished carbonproduct of the following composition, % by mass:

    ______________________________________                                        carbon              0.05-0.3                                                  manganese           0.05-0.1                                                  silicon             traces                                                    aluminium           traces                                                    sulphur             up to 0.03                                                phosphorous         up to 0.025                                               iron                the balance.                                              ______________________________________                                    

The choice of the steelmaking plant depends on the requirements whichshould meet any particular kind of steel for multi-purpose applicationand can be made by the steel maker.

The semifinished carbon product is tapped from the steelmaking plantinto a ladle of a capacity which corresponds to, or is a multiple of,that of the plant. Concurrently with pouring the semifinished carbonproduct into the ladle, fed thereinto are ferroalloys or a materialcontaining the alloying elements in the form of oxides and also thedisclosed material for refining steel of multi-purpose application. Allthese materials should be added before the pouring operation is over.

Used as oxide sources can be materials containing oxides of manganesemchromium, vanadium and titanium. They can be fed into the ladleseparately or in various combinations depending on the specifiedcomposition of the steel which should be obtained.

The ladle reduction of the alloying elements from the oxides is a shortprocess which comes practically to an end by the time the pouring of thesemifinished carbon product is finished. The percentage recovery of thealloying elements is up to 90-97%.

The desulphurization and removal of other nonmetallic inclusions goes onconcurrently with the alloying and is completed at the end of thepouring. This improves product quality and saves costs.

The disclosed refining material, if used in ladle alloying steel ofmulti-purpose application in conjunction with ferroalloys, also adds toproduct quality, but to a lesser extent. The explanation is that intapping the semifinished carbon product from the steelmaking plant, someslag enters the ladle from the furnace. The heavily oxidizedfurnace-originated slag not only brings about extra burning out of thedeoxidizer but impedes desulphurization so that the content ofnonmetallic inclusions rises. The totally reduced phosphorus of the slagpasses over into the steel. Any attempt to isolate the furnace slag andto fuse a new one from self-melting slag-making mixtures, or to usesynthetic slag, complicates the process and impairs plant capacity.Causing also an increase in costs, this practice not always turns toadvantage in making steel of multi-purpose application.

Therefore, it is preferred to employ the disclosed refining materialwhen the alloying is carried out by a recourse to oxides.

Since the disclosed refining material and the material containing thealloying oxides are added in the course of pouring the semifinishedcarbon product into the ladle, only a minimum of the elements with ahigh affinity for oxygen, present in the disclosed refining material, issubjected to burning out. In melting during the pouring, the materialcontaining oxides of the alloying elements forms a layer of slag at thesurface of the molten semifinished carbon product which isolates thedisclosed refining material from the oxygen of the atmosphere. A deeplydeoxidized metal lending itself readily to desulphurization is produced,the product quality is improved.

The disclosed material for refining steel of multi-purpose applicationcan be prepared in the form of a mixture comprising calcium carbide,silicon carbide and an aluminium-magnesium-iron alloy. This mixturelends itself to streamlined production better than the mixtures whereinthe components are present in a pure form with a maximum content of theprincipal element; it is also cheaper.

The silicon carbide used for preparing the mixture was of the followingcomposition, % by mass: SiC, 97.82; Si, 0.17; SiO₂, 0.12; Al₂ O₃, 0.9;Fe₂ O₃, 0.43; CaO, 0.3; MgO, 0.26. The composition of the calciumcarbide was in % by mass: CaC₂, 78.9; CaO, 17.3; Al₂ O₃, 1.6; SiO₂, 0.8;Fe₂ O₃, 0.5; MgO, 0.9.

The aluminium-magnesium-iron alloy was prepared by fusing the aluminiumand magnesium at 600°-650° C. in a basic-lined induction furnace, usinga crucible. The temperature was then increased to 1000°-1100° C. and aninert gas was fed onto the surface of the melt before the iron was addedbatchwise thereto. On allowing the iron to dissolve, the melt was cooledto 550°-600° C. and poured on cast iron trays. A comminution of thealloy to a specified particle size completed the preparation.

To prevent oxidation of the magnesium and aluminium, the alloy can beproduced in a vacuum induction furnace.

The disclosed refining material can also be employed in the form of analloy. Firstly, this simplifies storage, processing and the feeding ofthe material into the ladle. It is neither hygroscopic as calciumcarbide nor highly abrasive as silicon carbide which needs specialmixers. Secondly, the refining material provided in the form of an alloyis homogenous, i.e. of uniform chemical composition, and has a uniformdensity. A stability of the ladle refining process is guaranteed in thiscase. Thirdly, the composition of the alloy provides a means ofcontrolling the reactivity of the components towards oxygen, sulphur andnonmetallic inclusions.

The melting and pouring techniques and the temperatures used areidentical with those employed in preparing the aluminium-magnesium-ironalloy.

The charge material was as follows:

aluminium of a composition, % by mass: Al, 99.8; Fe, 0.12; Si, 0.01; Cu,0.01; Zn, 0.04; Ti, 0.02;

crystalline silicon of a composition, % by mass: Si, 98.8; Fe, 0.5; Al,0.5; CaO, 0.2;

metallic calcium of a composition, % by mass: Ca, 98.96; Al, 0.1; Mg,0.5; Mn, 0.05; N, 0.06; oxygen, 0.3; Fe, 0.01; Si, 0.02;

metallic magnesium of a composition, % by mass: Mg, 98.6; Ca, 0.3; Al,0.5; Si, 0.2; Mn, 0.1; Cu, 0.3;

carbon in the form of scrapped graphitised electrodes of a composition,% by mass: C, 98; loss of ignition, 2;

iron of a composition, % by mass: Fe, 99.5; C, 0.1; S, 0.003; P, 0.005;Mn, 0.2; Si, 0.022; Cu, 0.07; Zn, 0.1;

misch metal of a composition, % by mass: rare-earth elements, 98; iron,the balance.

To save cost and simplify the melting technique, the charge can beprepared from other components, e.g.:

silico-calcium of a composition, % by mass: Ca, 31; Si, 65; Fe, 3; Al,1;

ferro-silicon of composition, % by mass: Si, 90; Mn, 0.2; Cr, 0.2; P,0.03; S, 0.02; Al, 3.5; Fe, 6.05;

and other materials of suitable composition and competitive cost.

The disclosed percentage of aluminium and silicon in the material forrefining steel of multi-purpose application provides for producing adeeply deoxidized metal.

This promotes good desulphurization and provides for reducing thealloying element from their oxides with a maximum percentage recovery.Complex aluminate and silicate nonmetallic inclusions which form in thiscase are low-melting compounds which readily rise to the surface andpass there over into the slag without impairing its physical andchemical properties (melting point, fluidity, viscosity, the sorption ofsulphur and other nonmetallic inclusions, etc.).

A departure from the disclosed aluminium and silicon content of therefining material badly influences the process of deoxidation so thatthe degree of desulphurization of the metal consequently decreases. Alsoless alloying elements will be reduced from their oxides due to analtered behaviour of the slag. Its capacity as the sorbent will stepdown because its fluidity will decreases while the viscosity and meltingpoint will increase. The steel treated with such material will containmuch sulphur and other nonmetallic inclusions and its mechanicalproperties will be low.

The calcium and magnesium present in the disclosed refining material inthe disclosed amounts provide for desulphurizing the metal and modifyingthe nonmetallic inclusions in the course of pouring the metal into theladle. This yields quality steel.

An altering of the calcium and magnesium content above or below thespecified level impairs the refining effect. The sulphur contentincreases, coarse nonmetallic inclusions are formed, being distributednonuniformly. Low-grade steel is consequently produced.

The carbon contained in the disclosed refining material in the disclosedamount serves not only as the alloying element but takes part, to acertain extent, in the deoxidation process and promotesdesulphurization. The content of nonmetallic inclusions appears to bethen at a minimum, for the carbon monoxide formed due to the reactionbetween the carbon and the oxygen dissolved in the metal escapes withouthindrance. The film of each CO bubble is a surfactant which absorbsnonmetallic inclusions and disposes them of into the slag.

A carbon content which is below the specified one makes an additionalcarbonization of the metal indispensable. This interferes withstreamlined processing of metal and degrades product quality. A too highcarbon content limits the field of application of the disclosed refiningmaterial, rendering it unsuitable for the treatment of low-carbon steel.Also, the percentage of other components decreases in the materialwhereas that of sulphur and other nonmetallic inclusions increases,affecting product quality. A low degree of reduction of the alloyingelement makes the production of steel of a specified composition aproblem.

The disclosed amount of iron imparts an adequate density to thedisclosed refining material and increases the carbon content thereof.

Any altering of the iron content above or below the specified quantityimpairs product quality if the steel is treated with the disclosedrefining material. A consequent burning out of the elements which arereactive towards oxygen lessens the amount of desulphurization, impairsthe reduction of alloying elements and the modification of nonmetallicinclusions.

A preferred embodiment of the invention will now be exemplified asfollows.

EXAMPLE 1

The disclosed material for refining steel of multi-purpose applicationwas employed for alloy treatment, using a 350-t teeming ladle with abasic lining.

A semifinished carbon product with a composition (% by mass) of C, 0.05;Si, traces; Mn, 0.05; S, 0.014; P, 0.012; Al, traces; Fe, the balancewas tapped from an oxygen blown converter into the ladle at 1640° C.Concurrently, added into the ladle was a heat-treated material rich inmanganese protoxide which contained (% by mass) MnO, 53.6; SiO₂, 29.1;Fe₂ O₃, 3.9; Al₂ O₃, 3.3; P₂ O₅, 0.83; CaO, 6.6; MgO, 2.1; C, 0.4; S,0.17. Also added into the ladle at the same time was the disclosedrefining material comprising (% by mass) Al, 40; Si, 35; Ca, 5; Mg, 7;C, 10; Fe, the balance. Both additives were introduced into the ladlebefore the pouring of the semifinished carbon product came to an end.

The heat-treated material rich in manganese protoxide was added in atotal amount of 3.8 t, and the material for refining the steel ofmulti-purpose application, according to the invention, was used in aquantity needed to reduce the manganese protoxide and refine the steel.

This was of a composition (% by mass) as follows: C, 0.11; Mn, 0.49; Si,0.21; S, 0.003; P, 0.014; Al, 0.024; Fe, the balance. The percentagerecovery of manganese amounted to 98.2% and the degree ofdesulphurization was 78.6%.

The finished steel was poured into a bent-strand continuous castingmachine producing a strand with a cross section of 350 by 1650 mm. Thestrand was cut into billets and these were rolled into plate between 10and 30 mm thick. The macrodistribution of nonmetallic inclusions in theplate, as determined by metallographic studies in points was: oxides,1.4; sulphides, 1.6; silicates, 2.1. Quality steel with a low content ofsulphur and nonmetallic inclusions was obtained.

EXAMPLE 2

Alloy treatment of metal was confined to the same ladle as in Example 1,using the disclosed material for refining steel of multi-purposeapplication. The additives were the same as in Example 1.

The semifinished carbon product comprising (% by mass) C, 0.05; Si,traces; Mn, 0.05; S, 0.015; P, 0.014; Al, traces; Fe, the balance waspoured from an oxygen blown converter into the basic-lined teemingladle. Concurrently with the pouring, manganese-rich oxide material wasintroduced into the ladle together with the disclosed material forrefining steel of multi-purpose application which was a mixture ofcalcium carbide, silicon carbide and aluminium-magnesium-iron alloy. Thetotal composition (% by mass) of the refining material was: Al, 30; Si,30; Ca, 10; Mg, 5; C, 20; Fe, the balance.

The steel produced was of the following composition, % by mass: C, 0.12;Si, 0.19; Mn, 0.46; S, 0.005; P, 0.015; Al, 0.02; Fe, the balance. Thepercentage recovery of manganese amounted to 91.4% and the degree ofdesulphurization was 66.7%.

The steel was poured into a bent-strand continuous casting machineproducing a strand with a cross section of 350 by 1650 mm which was cutinto billets rolled wherefrom was plate between 10 and 30 mm thick. Themacrodistribution of nonmetallic inclusions in the plate, as determinedby metallographic studies, was (in points): oxides, 1.5; sulphides, 1.7;silicates, 2. Quality steel with a low content of sulphur andnonmetallic inclusions was obtained.

EXAMPLE 3

Metal was treated with the material for refining steel of multi-purposeapplication and the finished steel was poured in the same way as inExamples 1, 2, using the same additives.

The semifinished carbon product produced in an oxygen blown converterwas of the composition, % by mass: C, 0.06; S, traces; Mn, 0.004; S,0.016; P, 0.015; Al, traces; Fe, the balance.

The finished steel was of the composition, % by mass: C, 0.11; Si, 0.19;Mn, 0.48; S, 0.006; P, 0.015; Al, 0.025; Fe, the balance. The percentagerecovery of manganese amounted to 97.6% and the degree ofdesulphurization was 62.5%.

The macrodistribution of the nonmetallic inclusions (in points) was:oxides, 1.6; sulphides, 1.8; silicates, 1.8. Quality steel with a lowcontent of sulphur and nonmetallic inclusions was obtained.

EXAMPLE 4

The treatment was carried out with the disclosed material for refiningsteel of multi-purpose application which was a mixture of thecomposition (% by mass) as follows: Al, 30; Si, 35; Ca, 5; Mg, 7; C, 20;Fe, the balance.

The melting, refining and pouring techniques were the same as inExamples 1 through 3.

Treated in the ladle was a semifinished carbon product of thecomposition, % by mass: C, 0.04; Si, traces; Mn, 0.05; S, 0.015; P,0.015; Al, traces; Fe, the balance, which had been produced in an oxygenblown converter.

The steel so produced was of the following composition, % by mass: C,0.09; Si, 0.21; Mn, 0.48; S, 0.006; P, 0.016; Al, 0.021; Fe, thebalance. The percentage recovery of manganese amounted to 95.4% and thedegree of desulphurization was 60%.

The macrodistribution of the nonmetallic inclusions was (in points):oxides, 1.5; sulphides, 1.9; silicates, 2.

EXAMPLE 5

Chromium-alloyed steel was treated in a teeming ladle, using converterslag as the chromium-containing oxide material. The slag composition (%by mass) was as follows: Cr₂ O₃, 70.84; FeO, 12.13; Al₂ O₃, 9.35; SiO₂,5.94; MgO, 1.74.

The slag-forming ingredients were lime and fluorspar.

A semifinished carbon product of the composition, % by mass: C, 0.06;Si, traces; Mn, 0.08; S, 0.026; P, 0.012; Al, traces; Cr, 0.1; Ni, 0.59;Cu, 0.51; Fe, the balance, was tapped from a converter into thebasic-lined ladle at 1650° C.

Concurrently with pouring the semifinished carbon product, admitted intothe ladle were 13.5 t of the chromium-containing oxide material, 1.5 tof the lime and 0.02 t of the fluorspar. Also admitted into the ladlewas the disclosed material for refining steel of multi-purposeapplication in the form of an alloy of the composition, % by mass: Al,37; Si, 25; Ca, 15; Mg, 7; C, 12; Fe, the balance. Other alloyingelements were introduced by adding ferroalloys.

The steel so produced was of the composition, % by mass: C, 0.1; Si,0.95; Mn, 0.62; Al, 0.035; S, 0.007; P, 0.015; Cr, 0.87; Ni, 0.59; Cu,0.51; Fe, the balance. The percentage recovery of chromium amounted to86.2%, and the degree of desulphurization was 73.1%.

The billets produced on a continuous-casting machine were rolled intoplate as in Examples 1 and 2, and the plate was subjected tometallographic studies. These have shown that the content of nonmetallicinclusions was less than in previous examples, proving a better qualityof the product. The content of nonmetallic inclusions (in points) was:oxides, 1.5; sulphides, 1.8; silicates, 1.9.

EXAMPLE 6

Metal was treated and poured in the same way as in previous examples,using the same materials as in Example 5.

The semifinished carbon product produced in an oxygen blown converterwas of the composition (% by mass) as follows: C, 0.06; Si, traces; Mn,0.05; S, 0.022; P, 0.012; Al, traces; Cr, 0.13; Ni, 0.68; Cu, 0.55; Fe,the balance. In pouring the carbon product into the teeming ladle, addedthere into was the material for refining steel of multi-purposeapplication in the form of a mixture comprising, % by mass: Al, 35; Si,30; Ca, 7; Mg, 5; C, 20; rare-earth elements, 1; Fe, the balance.

The product was steel of the following composition, % by mass: C, 0.12;Si, 1.01; Mn, 0.73; S, 0.007; P, 0.013; Al, 0.023; Cr, 0.9; Ni, 0.68;Cu, 0.55; Fe, the balance. The percentage recovery of chromium amountedto 96.2%, and the degree of desilphurization was 68.2%.

The metallographic studies of the finished steel revealed the followingcontent of nonmetallic inclusions (in points): oxides, 1.6; sulphides,1.7; silicates, 1.6. The inclusions were present in the fine globularform.

EXAMPLE 7

The chromium-containing material for refining steel of multi-purposeapplication was fed into a teeming ladle in the course of pouringthereinto a semifinished carbon product which was produced in an oxygenblown converter and was of the composition (% by mass) as follows: C,0.05; Si, traces; Mn, 0.05; S, 0.021; P, 0.015; Al, traces; Cr, 0.1; Ni,0.69; Cu, 0.53; Fe, the balance.

In use were the same chromium oxide-containing and slag-formingmaterials as in Examples 5 and 6.

Also in use was the disclosed material for refining steel ofmulti-purpose application in the form of a mixture of calcium carbide,silicon carbide and an alloy containing aluminium, magnesium, rare-earthelements and iron. The content of the refining material was as follows,% by mass: Al, 30; Si, 28; Ca, 15; Mg, 6; C, 10; rare-earth elements, 3;Fe, the balance.

The treatment was finished by the time the pouring of the semifinishedcarbon product into the ladle was over.

The steel so produced was of the composition, % by mass: C, 0.1; Si,1.08; Mn, 0.72; S, 0.007; P, 0.015; Al, 0.024; Cr, 0.87; Ni, 0.69; Cu,0.53; Fe, the balance. The percentage recovery of chromium amounted to96.2%, and the degree of desulphurization was 66.7%.

The metallographic studies of the steel showed the following content ofnonmetallic inclusions (in points): oxides, 1.4; sulphides, 1.6;silicates, 1.7. The inclusions were present in the fine globular form.

EXAMPLE 8

Used were the same chromium oxide-containing and slag-forming materialsas in Examples 5 through 7. The technique of melting, treating andpouring was the same as in these Examples.

The semifinished carbon product subjected to the refining was of thecomposition, % by mass: C, 0.05; Si, traces; Mn, 0.07; S, 0.022; P,0.013; Al, traces; Cr, 0.1; Ni, 0.68; Cu, 0.53; Fe, the balance.

The disclosed refining material was used in the form of an oxidematerial of the composition (% by mass) as follows: Al, 40; Si, 26; Ca,10; Mg, 6; C, 12; rare-earth elements, 5; Fe, the balance.

The refined steel was of the following composition, % by mass: C, 0.1;Si, 1; Mn, 0.73; S, 0.006; P, 0.013; Al, 0.026; Cr, 0.88; Ni, 0.68; Cu,0.53; Fe, the balance. The percentage recovery of chromium amounted to97.5%, and the degree of desulphurization was 72.7%.

The steel, on being poured and rolled, was subjected to metallographicstudies which showed that the content of nonmetallic inclusions (inpoints) was as follows: oxides, 1.7; sulphides, 1.4; silicates, 1.6.

Quality steel was produced with a low sulphur content. The nonmetallicinclusions were in the form of fine globules uniformly distributed overthe volume of the metal.

EXAMPLE 9

Steel of multi-purpose application was alloyed with manganese, using thedisclosed refining material in the form of an alloy of the composition,% by mass: Al, 32; Si, 35; Ca, 8; Mg, 7; C, 11; rare-earth elements,1.5; Fe, the balance.

The manganese-containing oxide material was of the same content as inExample 5 and was added in the same amount.

The semifinished carbon product subjected to the refining was of thefollowing composition, % by mass: C, 0.05; Si, traces; Mn, 0.05; S,0.016; P, 0.015; Al, traces; Fe, the balance.

The steel so obtained was of the composition, % by mass: C, 0.1; Si,0.22; Mn, 0.48; S, 0.005; P, 0.015; Al, 0.022; Fe, the balance. Thepercentage recovery of manganese was 95.6%, and the degree ofdesulphurization was 68.8%.

The content of nonmetallic inclusions (in points) was: oxides, 1.4;sulphides, 1.7; silicates, 1.9.

EXAMPLE 10

A semifinished carbon product containing in % by mass C, 0.06; Si,traces; Mn, 0.05; S, 0.018; P, 0.015; Al, traces; Fe, the balance wasrefined with the disclosed material in the form of an alloy of thecomposition (% by mass) as follows: Al, 38; Si, 28; Ca, 10; Mg, 7; C,12; rare-earth elements, 2; Fe, the balance.

Other materials used for the alloy treatment were the same as inExamples 1 through 4 and 9.

The steel produced was of the composition, % by mass: C, 0.1; Si, 0.18;Mn, 0.47; S, 0.006; P, 0.015; Al, 0.021; Fe, the balance. The percentagerecovery of manganese amounted to 93,2%, and the degree ofdesulphurization was 66.7%.

The steel was poured, rolled and examined metallographically in the sameway as in Example 1.

The content of nonmetallic inclusions (in points) was as follows:oxides, 1.5; sulphides, 1.7; silicates, 1.8.

Quality steel with a low-sulphur content which also containednonmetallic inclusions in an advantageous form and of a favourablestructure was produced in this way.

INDUSTRIAL APPLICABILITY

The present invention will turn to advantage in refining steel when itsalloying is carried out by reducing the alloying element from anoxide-containing material as this is the case, e.g. in ladle refiningmanganese steel of multi-purpose application. The degree ofdesulphurization is 60-80%, and the content of nonmetallic inclusions(in points) is: oxides, 1-2; sulphides, 1-2; silicates, 1.5-2.5.

We claim:
 1. A material for refining steel of multi-purpose application,containing aluminum, silicon, calcium, magnesium, carbon and iron,characterized in that it contains said components in the followingproportions, % by mass:

    ______________________________________                                        aluminium     30-40                                                           silicon       35-25                                                           calcium        5-15                                                           magnesium     7-5                                                             carbon        20-10                                                           iron          the balance.                                                    ______________________________________                                    


2. A material as claimed in claim 1, characterized in that it containsadditionally rare-earth elements and incorporates the components in thefollowing proportions, % by mass:

    ______________________________________                                        aluminium        30-40                                                        silicon          30-25                                                        calcium          15-5                                                         magnesium        5-7                                                          carbon           10-20                                                        rare-earth elements                                                                            5-1                                                          iron             the balance.                                                 ______________________________________                                    


3. A material as claimed in claim 1, characterized in that it containsadditionally rare-earth elements and incorporates the components in thefollowing proportion, % by mass:

    ______________________________________                                        aluminium        30-40                                                        silicon          35-25                                                        calcium          15-5                                                         magnesium        5-7                                                          carbon           10-12                                                        rare-earth elements                                                                            1-2                                                          iron             the balance.                                                 ______________________________________                                    